One method to correct sensed position of an internal combustion is described in U.S. Pat. No. 5,692,488. This method presents a way to correct engine sensor data from a bottom-dead-center (BDC) marker signal by using information gathered from a determined engine position. Then the BDC correction is used to adjust the location of other engine angle markers. Specifically, the BDC marker is corrected based on an assumption that the maximum cylinder air charge occurs when an intake valve closes at BDC and that the valve closing location that corresponds to BDC can be determined based on the maximum cylinder air charge. Consequently, the method attempts to find an intake valve closing time that results in the maximum cylinder air charge for a set of engine operating conditions. In one example, the method attempts to determine maximum cylinder charge for a selected intake valve closing time from fuel injection time and exhaust gas oxygen concentration. Alternatively, the method may use a constant injection time and vary intake valve closing timing to establish the valve timing that produces the leanest exhaust air-fuel mixture. The intake valve closing position associated with the maximum cylinder air charge is then used as the location of BDC.
The above-mentioned method can also have several disadvantages. In particular, the method merely corrects the BDC marker position and then applies this correction to other engine angle markers. In other words, the method appears to acknowledge that factors such as manufacturing variation can produce variation between an engine position and a specific BDC marker, but the method assumes that this same error applies to other engine angle markers. For example, it can be possible that engine angle markers are not accurately spaced nor perfectly symmetrical (i.e., the high and low portions of the other engine angle marker signals are not uniform over an entire engine revolution). These types of irregularities may produce inter-teeth engine position detection variation (i.e., measurement errors between engine angle markers). In addition, other factors can also affect engine position detection such as speed dependant sensor measurement error, variation of wheel diameter, and the distribution of ferrous metal in the wheel. Further, the method relies on the assumption that maximum cylinder air charge occurs when intake valves are closed at BDC. However, this assumption may be invalid if the cylinder residual gas fraction is changed or if the inertia of the cylinder air charge causes the maximum cylinder air charge valve timing to be at a location other than BDC.
Another method to correct sensed position of an internal combustion engine is described in U.S. Pat. No. 5,611,311. This method compares a phase difference between a determined top-dead-center engine position and a referenced engine position sensed by a crank angle sensing means, to a predetermined value, and attempts to correct the crank angle position sensed by the crank angle sensing means by using a deviation of the crank angle phase difference from the predetermined value. In other words, a reference position can be compared to a determined engine position so that an offset (measured in crank angle degrees) may be determined. This offset can then be combined with sensed crank angle position to estimate actual engine position.
This method can also have several disadvantages. For example, similar to the previously mentioned method, this method attempts to account for measurement offset from an engine position, namely top-dead-center. However, this method also fails to correct for variations between sensed engine angles. Further, the method may be costly and/or impractical to implement on an engine since the method relies on a cylinder pressure sensing device to determine the engine angle correction amount.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of correcting engine position that offers substantial improvements.